"Catholic Terrorist Group the Irish Republican Army"
"Fundamentalist Christian Terrorist Group the Klu Klux Klan"
Now come on, both the above sounds down right silly. But yet if you follow the logic of naming terrorist groups based on a religious affiliation, the above tags are at least consistent...if, all be it, not used.
Now in some circles, the President gets a lot of grief for refusing to refer to groups like ISIS/ISIL (or whatever the heck they are called) as "Islamic Terrorists". His explanation for the refusal, as far as I have heard it, is a good one: By using that tag, the implication is that potentially anyone who is an adherent of Islam is a terrorist. The President is right, period.
Could you argue "But, but, but Steve, Islamic clerics provide religious justification for groups like ISIS/ISIL, so the tag of Islamic Terrorist fits!" ? Sure, you could, but that argument just doesn't hold water. As proof, I offer the following:
Catholic Priests Played A Role In IRA Killings
IRA Bombing Priest
KKK: We's a Christian Organization
...and that's just the first bit of the first page of the Google search.
Yes, many terrorist groups cloak themselves in Islam, but that doesn't mean that these terrorist groups are "Islamic"...no more so than Irish Catholic groups in, say, Boston are all supporters of the Irish Republican Army. What's more, I know that the vast majority of Catholic clergy would never support the murderous activities of the IRA, just as the vast majority of Pentecostal and Baptist ministers would never support the actions of the KKK either.
Also, there is no central religious authority for Islam to condone or condemn terrorist actions. The religion itself is split into various groups act sects, not unlike modern Christianity. This is another reason why the labeling of terrorists as "Islamic" is simply wrong, because no one person can speak for Islam, just as Pope Francis can not speak for all of Christianity. I do agree though that moderate Islamic voices have not nearly been loud enough in condemning the actions of these evil groups, which is a shame, as they have the most to lose (and in fact ISIS/ISIL has probably killed more "fellow" Muslims than members of any other group).
To the extent one chooses to judge others, and I'll note that is a risky endeavor right off the bat, it's important to at least attempt to be factually correct and consistent. Throwing labels around like "Islamic Terrorist Group" fails both the "factually correct" and "consistent" tests.